Wireless broadband provider Clearwire announced this week that it is has secured another $920 million in debt to help it finance continued construction of its 4G wireless network, which is being rolled out across the globe.

The $920 million comes from 12 percent senior secured notes, due 2015 at an issue price of 97.9 percent. This offering comes on top of another $1.85 billion in senior secured notes also due in 2015. The notes will be guaranteed by Clearwire's (NASDAQ: CLWR) wholly owned domestic subsidiaries.

Building a global network from scratch isn't cheap. All told, the $2.8 billion Clearwire has raised in recent weeks will go toward paying off an existing $1.4 billion debt payment and be used to fund continued infrastructure expansion.

"With this latest tranche of additional funding, we have not only exceeded the amount of capital that we have previously stated we needed to fully fund our business plan, but we have also secured additional capital that will allow us to expand more aggressively by covering more people, and with more capacity than we had previously planned," Clearwire CEO Bill Morrow said in a statement.

Clearwire is the creation of Craig McCaw, one of the early cellular pioneers who sold his network to AT&T in 1994. He started Clearwire in 2003 as a wireless Internet service provider to serve markets in the United States, Ireland, Belgium, Spain, Denmark and Mexico. It is built using pre-WiMAX technology but after merging with Sprint's 4G wireless network in 2008 has added WiMAX support.

In addition to the independent funding, Clearwire has also gotten $1.5 billion in investor funding from Sprint Nextel, Intel (NASDAQ: INTC), Comcast, Time Warner Cable and Google (NASDAQ: GOOG).

Clearwire said earlier this year that it needed an additional $2 billion to $2.3 billion in funding to ensure its network could reach at least 120 million people by the end of 2010. Thus far, it's only available in a few cities, including Chicago, Baltimore, Portland, and Philadelphia.

The competition is fierce: Verizon Wireless is building its own 4G wireless network, T-Mobile is upgrading its networks to match Clearwire's 3Mbit/sec. speed and AT&T has its own 3G network.

As a result, it's slow growth for Clearwire. As of second quarter, Clearwire has a total subscriber base of 550,000, and that includes consumers who have signed through Clearwire's reseller partners Sprint, Comcast, and Time Warner Cable.